This program of research is designed to continue the attempt to develop a variety of model systems in Aplysia in which one can combine cellular electrophysiological, morphological, biochemical and behavioral techniques to study the mechanisms of behavior and its modification. The specific aim is to examine the cellular mechanisms of different behavioral modifications controlled by the abdominal ganglion of Aplysia so as to be able to specify the relationships between them. Toward that end we plan, in the proposed research, to carry out four interrelated studies: 1) Studies on the mechanistic interrelationships, of different behavioral modifications of the gill-withdrawal reflex: a) the relationship between short- and long-term habituation and sensitization; b) the interactions between long-term habituation and long-term sensitization; and c) the effects of state variable on the acquisition and retention of long-term habituation and sensitization. 2) Behavioral and cellular neurophysiological studies of two other behavioral systems controlled by the abdominal ganglion: a) neural control of inking behavior; and b) neural control of the circulation. 3) Studies on the effects of modification in one behavioral system, controlled by the abdominal ganglion, on the responsiveness of another. 4) Studies on the development of behaviors controlled by the abdominal ganglion of Aplysia and the correlation of the behaviors with the development of their neural circuits.